Process for fixing lithographic diazotype printing foils having been exposed to light



PROCESS FOR FIXING LITHOGRAPHC DIAZO- TYPE PRINTING FOHS HAVING BEEN EX-POSED TO LIGHT Wilhelm Neugebauer, Wiesbaden-Biebrich, and JakobBarthenheier, Eddersheim on Main, Germany, assignors, by mesneassignments, to Azoplate Corporation, Summit, N. J., a corporafion ofNew Jersey N Drawing. Application December 3, 1951, Serial No. 259,712

Claims priority, application Germany December 8, 1950 9 Claims. (Cl.955.4)

This invention relates to a new process of fixing photosensitivelithographic printing plates. More particularly, the invention pertainsto fixing photosensitive foils provided with a light-sensitive layerfree from hardenable colloid substances and sensitized by means of aspecific group of diazo compounds. The plates are produced by exposingthe photosensitive foils to light under a master and fixation of theexposed foils has the purpose of stabilizing the printing plates againstthe further influence of light.

The diazo compounds mentioned above are selected from the groupconsisting of: (l) the diazo compounds corresponding to the formula R1wherein X stands for an equivalent of an anion of an acid Ar stands foran aromatic residue R stands for a member of the group consisting ofaryl, aralkyl and aroyl with the inclusion of the substituted members ofeither R1 stands for a member of the group consisting of H,

alkyl, aryl and aralkyl (2) condensates thereof with aldehydes, (3)sulfonates of (1), and (4) sulfonates of (2).

The co-pending patent application of Wilhelm Neugebauer and JakobBarthenheier, Serial No. 70,802, now Patent Number 2,626,866, issued onJanuary 27, 1953, filed January 13, 1949, describes a process for thefixation of this type of planographic and offset printing plates whichhave been produced by exposing the above characterized light-sensitivematerial to a light image. This may be accomplished by exposing to lightunder a master or by exposing to a projected image. The fixing effect isobtained by tWo essential steps. Subsequent to the exposure of thematerial to a light image, the exposed surface is coated with a layer ofa water-soluble organic colloid substance by treating the surface of thematerial with an aqueous solution containing a water-soluble organiccolloid substance and then subjected once more (with or withoutintermediate drying) to an exposure which this time is an overalluniform exposure of the entire surface (i. e., without using anoriginal). The printing plates treated in this manner, when rubbed inwith greasy ink in the presence of water, take greasy ink only at thoseareas that were struck by light during the first exposure under amaster, while they do not take the greasy ink at the other areas. Thelatter areas have been rendered hydrophilic by the second exposurebecause they have been struck by light under the coating consisting of awater-soluble colloid substance.

It has now been found that the fixation can be effected also by firstapplying greasy ink and water to the surface of the foil immediatelyafter it was exposed to light under a master (this can be done byswabbing the surface with ink after the surface has been sprayed Withwater, or by wetting a cotton swab with water and then placing somegreasy ink on it and swabbing the surface, or by other analogous manualmeans, or in an offset printing machine using the inked rollers as willbe readily understood by those skilled in the art) then subsequentlyapplying a water-soluble coating of the type disclosed in the copendingapplication referred to above and reexposing the foil (with or Withoutintermediate drying) without a master. Printing plates are obtained thatare insensitive to further action of light and they take greasy ink onlyat the places affected by light during the first exposure. The practicalresults achieved by this working procedure frequently are especiallygood.

The following examples are inserted in order to illustrate the presentinvention:

(1) A superficially saponified foil of cellulose acetate is coated witha 3% aqueous solution of the zinc chloride double salt of the diazocompound obtained from 1 mole of p-diazo-diphenylamine and 1 mole ofparaformalde hyde by their condensation in sulfuric acid of 60 B. and isthen dried after the excess solution has been Wiped off. The foil isexposed under a negative master and subsequently is rubbed in Withgreasy ink in the presence of water. The areas of the foil struck bylight accept the greasy printing ink. The application of the greasyprintingink can be performed also in an offset printing ma- Due to thepresence of the light-sensitive diazo chine. compound at the places thatwere not struck light, the foil is still light-sensitive at this stage.Consequently it tends to take greasy ink also at the places that werenot struck by light during its exposure under the master when it isexposed to the action of light subsequent to the appli cation of theink. In order to fix the printing plate permanently and render itinsensitive to the action of light, the foil is wiped over with an 8%aqueous solution of dextrine and is reexposed Without a pattern; thediazo compound still present is thereby decomposed, but formshydrophilic products not hydrophobic oleophilic decomposition products.After the dextrine has been washed oh, the foil can be used forprinting.

The foil is now insensitive to further action of light. In place of thedextrine solution, solutions of other watersoluble colloids may be used,such as, for example, solutions of gum arabic, of polyvinyl alcohol, ofmethylcellulose, preferably with low viscosity, of salts ofcurboxy-methylcellulose, of sodium alginate, of polyvinyl pyrrolidone,of pectin, of a watersoluble urea-formaldehyde resin, of guar resin, ofpeptone of albumin, etc.

(2) A superficially saponified acetyl-cellulose foil is rubbed in with a6% aqueous solution of the sulfate of the diazo compound derived from4-amino-N-2',6-dichlorobenzylaniline which still contains 5% glycerine,and is then dried. Subsequent to its exposure under a negative, thelayer side of the foil is rubbed in with greasy ink in the presence ofwater and wiped over with an 8% aqueous dextrine solution, then it isdried and reexposed without a master. The dextrine is washed off withwater and the foil is clamped to an offset printing machine. It is onlyink receptive at areas that were struck by light during the exposureunder the master and at areas to which the dextrine solution was notapplied. 0n the other hand, at the unexposed areas that were coated withthe dextrine solution during the reexposure, it bears water and expelsgreasy printing ink.

(3) A parchment paper foil backed with a cardboard base is evenly coatedwith a 3% aqueous solution of the condensation product prepared from 1mol of p-diazodiphenylamine and 1 mol of formaldehyde in sulphuric acidof 60 B6. and is dried thereafter with hot air.

The light-sensitive layer is exposed to light for-- l -minute under anegative master, e. g. with the aid of an 18 ampere arc lamp 'at' a'distance of 70 'cm'., the exposed material is then rinsed with water andthe surface of the layer is rubbed in with greasy ink. A positive imageis obtained which is wiped over with 220% aqueous solution of gum arabicand is dried'thereafter with hot air.

Then the inked surface is reexposed to light without a 70,802, nowPatent Number 2,626,866, issued on January 27, 1953, are used instead ofgum arabic and otherwise the'process is the same as described above,foils are obtained which also yield clear prints after the secondexposure to light.

(4) The process is the sameas described in Example 3 but instead of thediazo compound used in Example 3 the sulphate of the diazo compoundof'4-amino-N-(2,6-dichlorobenzyl)-aniline is used. The result is thesame'as in Example 3.

(5) A paper foil manufactured according to U. S. Patent 2,534,588 andsold commercially in the United States is sensitized with a 3% aqueoussolution of the sulphonate of the condensation product prepared from 1mol of diazo-diphenylamine and 1 mol of formaldehyde in sulphuric acidof 60 B. and the layer is dried thereafter with hot air. The dry layeris then exposed to light for 5 minutes under a negative master with theaid of'an 18 ampere-arc lamp at a distance-of 70cm. The layer is-'wipedover with a 5% aqueoussolution ofprimary ammonium phosphate and then theexposed layer is rubbed in with greasy ink. A positive'imag'e isobtained; Then the image is wiped over with a aqueous solution ofpolyvinyl alcohol of medium viscosity and the whole foil is reexposedwithout a master for 5 minutes with the aid of an arc lamp of 18 amperescurrent at a distance of 70 cm. Printing in an offset printing machineyields good prints on a clear background.

Having now described and disclosed the present invention, What we claimis:

1. In a process for making a lithographic printing material fromphotosensitive material sensitized with alight-sensitive diazo compoundselected from the group consisting of: (l) the diazocompou-ndscorresponding tothe formula wherein.

X stands for an equivalent of an anion of an acid Ar stands for anaromatic residue R stands for a member of the group consisting of aryl;aralkyl, and aroyl with the inclusion of thesubstituted members ofeither R1 stands for a member of the group consistingof H,

alkyl, aryl and aralkyl (2) condensates thereof with'ald'ehydes, (3)sulfonates of (l), and (4) sulfonates'of (2), by exposing the saidmaterial with a layer of saidwater-soluble colloid substance and thensubjecting'said coated material to-an overall exposure to light wherebysaid material iwill no longer be capable of being affected b'y-light'but upon removal of said water-soluble colloidsubstancesaidmate-' 4rialwillbe capable of functioning as a lithographic printing plate.

2. In' a" process for making" a" lithographic printing material fromphotosensitive material sensitized with a light-sensitive diazo compoundwhich upon exposure to light decomposes into a greasyink-receptivesubstance, by exposing the photosensitive surface of said material tolightthroughanoriginal, the fixing :method'compri'sing the stepsof firstapplying greasy ink and water to said light exposed surface,subsequently treating the inked surface with .an aqueous: solutioncontaininga water soluble organic colloid substance to'coat said.exposed and inked surface'of said material witha layer 'of'saidwatersoluble colloid substanceand then-subjecting'said coatedmaterial-to an overall exposure-to light whereby said material will nolonger be' capableofibeing affected by light but upon removal of saidwater-soluble colloid substance said material will be capable offunctioningas' a lithographic printing plate;

3. In a process for making a lithographic printing material-from aphotosensitive material sensitized with a light-sensitive diazocompound'which upon exposure to light decomposes into a greasyinkreceptive substance, by. exposing the photosensitive surface ofsaid'material to light through an original, the fixing method comprisingthe steps of first applying greasy ink and water to said lightexposed-surface, subsequently treating the inked surface with an aqueoussolution containing a water-soluble colloid substance selected from thegroup consisting of dextrine, gum arabic, cellulose ethers, polyuronicacids, and the salts thereof, polyvinyl alcohol, polyvinyl-pyrrolidones,water-soluble urea resins, protcins, polyethylene-oxide, pectin,sodiumalginate, mesquite gum and guar resin, to coat said exposed andinked surface of said material with a layer of said watersoluble colloidsubstance and then-subjecting said coated material to an overallexposure tolight, whereby said material will no longer be capable ofbeing affected by" light but upon removal of said Water-soluble colloidsubstance saidmaterial will be'capable' of functioning as a lithographicprinting plate. I

4'; In a process forrnakinga lithographic printing material, fromphotosensitive material' sensitized with a light-sensitive diazocompound which upon exposure to light decomposes into a greasyink-receptive substance; by exposing the photosensitive surface of"saidmaterial tov light through an original, the fixing methodcomprising the steps of first applying .greasy ink and water to saidlight exposed surface, subsequently. treating the inked-surface with anaqueous dextrinesolution to coat saidexposed and inked surface of saidmaterial with a layer-of: dextrine, and then subjectingsaid coatedmaterial to an overall exposure to light, whereby'said' material-Will nolonger be capable of being affected by light but upon removal of saiddextrine layer said mate rial layer will be capable of functioning as alithographic printing plate.

5. In a process for making a lithographic printing material, from aphotosensitive foil sensitized with a light-sensitive diazo compoundwhich upon exposure to light decomposes into-a greasy ink-receptivesubstance, by exposing the photosensitive surface of saidmaterial tolight through an original, the fixing method comprising the steps offirst applying greasy ink and-water to said lightexposed surface,subsequently treating the. inked surface withan aqueous protein solutiontocoat said exposed and inked surface of saidmaterial with a layer ofprotein, and then subjecting-said coated material to an overall exposureto light, whereby said-material will no longer be'capable' of beingaffected by' light but-upon removal of said protein layer said materialwillbe-capable of functioning as a lithographic printing plate.-

6. In a process for making; fl-llihOglfiPhlO printing material from aphotosensitive material sensitizedwith greases a light-sensitive diazocompound which upon exposure to light decomposes into a greasyink-receptive substance, by exposing the photosensitive surface of saidmaterial to light through an original, the fixing method comprising thesteps of first applying greasy ink and water to said light exposedsurface, subsequently treating the inked surface with an aqueoussolution of colloidal gum to coat said exposed and inked surface of saidmaterial with a layer of colloidal gum, and then subjecting said coatedmaterial to an overall exposure to right, whereby said material will nolonger be capable of being affected by light but upon removal of saidWater-soluble colloid gum layer said material will be capable offunctioning as a lithographic printing plate.

7. In a process for making a lithographic printing material from aphotosensitive material sensitized with a light-sensitive diazo compoundwhich upon exposure to light decomposes into a greasy ink-receptivesubstance, by exposing the photosensitive surface of said material tolight through an original, the fixing method comprising the steps offirst applying greasy ink and water to said light exposed surface,subequently treating the inked surface with an aqueous gum arabicsolution to coat said exposed and inked surface of said material with alayer of gum arabic, and then subjecting said coated material to anoverall exposure to light, whereby said material will no longer becapable of being aifected by light but upon removal of said gum arabiclayer said material will be capable of functioning as a lithographicprinting plate.

8. In a process for making a lithographic printing material from aphotosensitive material sensitized with a light-sensitive diazo compoundwhich upon exposure to light decomposes into a greasy ink-receptivesubstance, by exposing the photosensitive surface of said material tolight through an original, the fixing method comprising the steps offirst applying greasy ink and water to said exposed surface,subsequently treating the linked surface with an aqueous mesquite gumsolution to coat said exposed and inked surface of said material with alayer of mesquite gum and then subjecting said coated material to anoverall exposure to light, whereby said material will no longer becapable of being atfected by light but upon removal of said mesquite gumlayer said material will be capable of functioning as a lithographicprinting plate.

9. In a process for making lithographic printing material from aphotosensitive material sensitized with a light-sensitive diazo compoundwhich upon exposure to light decomposes into a greasy ink-receptivesubstance, by exposing the photosensitive surface of said material tolight through an original, the fixing method comprising the steps offirst applying greasy ink and water to said light exposed surface,subsequently treating the inked surface with an aqueous solution of guarresin to coat said exposed and inked surface of said material with alayer of guar resin, and then subjecting said coated material to anoverall exposure to light, whereby said material will no longer becapable of being affected by light but upon removal of said guar resinlayer said material will be capable of functioning as a lithographicprinting plate.

References Cited in the file of this patent UNITED STATES PATENTS2,311,889 Toland et al Feb. 23, 1943 2,313,848 Toland et al Mar. 16,1943 2,448,861 Colt Sept. 7, 1948 2,568,503 Kenyon et al. Sept. 18, 19512,626,866 Neugebauer et a1. Jan. 27, 1953

1. IN A PROCESS FOR MAKING A LITHOGRAPHIC PRINTING MATERIAL FROMPHOTOSENSITIVE MATERIAL SENSITIZED WITH A LIGH-SENSITIVE DIAZO COMPOUNDSELECTED FROM THE GROUP CONSISTING OF: (1) THE DIAZO COMPOUNDSCORRESPONDING TO THE FORMULA